In general, existing methods for removing noise of partial discharge signal can be divided into two ways: Noise gating method and Offset processing method. Both methods need for installing a partial discharge sensor and an independent noise sensor. The noise gating method gets rid of a peak of a partial discharge sensor signal, which is positioned at the same time interval as a time interval at which a peak detected from the noise sensor is positioned. On the other hand, the offset processing method adjusts a base noise level by adjusting an amplification degree.
In the noise gating method, the noise sensor and the partial discharge sensor are required to be in the same condition. However, since conditions such as a phase difference, sensor sensitivity, a distance from a noise generation point, sensor directivity, and attenuation of coaxial lines are different, the method of removing a peak value has substantially low efficiency in removing noise.
In the offset processing method, since a plurality of filtering circuits overlap in a front end of an RF processing analog circuit and suppress noise, an actually generated partial discharge signal may not be detected.
Meanwhile, devices for diagnosing partial discharge in the related art include an ultrasonic microphone sensor and a detection sensor that detect a pulse voltage and ultrasound generated when partial discharge of power equipment is generated, and thereby diagnose the partial discharge.
In this case, electromagnetic waves generated when the partial discharge is generated exit through a certain exit (a gasket and/or a spacer), the electromagnetic waves are represented as a pulse waveform having an amplitude of several mV and a rise time of several ns in ground potential of a metal enclosure of the power equipment, and the partial discharge is diagnosed by detecting this pulse waveform.
In this case, when an external electromagnetic wave generation source of a 1 GHz band, for example, a mobile phone and an RF transmitter, is in a direct current (DC) end, it exerts an influence on a result value and diagnostic reliability decreases.
In addition, the devices for diagnosing partial discharge in the related art detect the partial discharge by detecting ultrasound delivered over the air when the partial discharge is generated, and a center band of a microphone for ultrasound measurement is 40 kHz.
In this case, an air passage through which the ultrasound flows out is required to be provided. However, due to characteristics of the power equipment, since a structure manufactured with an iron enclosure does not include an outflow passage of the ultrasound, it is inappropriate. In addition, when there is ambient noise in excess of 40 kHz, diagnostic conditions are inappropriate, and thereby diagnosis is impossible. When there is strong ambient electrical noise, the ultrasound sensor may operate abnormally.